Synthesis and Raman Spectroscopy of Multiphasic Nanostructured Bi–Te Networks with Tailored Composition

Abstract

Development of synthetic routes to control the morphology and composition of nanostructured thermoelectric materials and to leverage their unique performance enhancements presents challenges in the realization of practical thermoelectric systems. We report here the fabrication of intricate networks of nanostructured tellurium, bismuth telluride, and bismuth-rich compounds with diverse morphologies. The nanostructured networks synthesized via solution-phase techniques consist of nanocrystalline Bi2Te3 with a grain size of about 15–20 nm, 3–5 nm thick rolled-up nanosheets of Te forming tubular structures, nanotubes of Bi2Te3 about 300–400 nm in diameter, Te and Bi4Te3 nanowires ranging from 50 to 200 nm diameter, and microspheres of 3–7 μm diameter composed of self-assembled BiOCl nanorods. The formation and crystallinity of Bi-rich and Te-rich compounds were investigated using powder X-ray and electron back-scattered diffraction. We present the first detailed analysis of micro-Raman scattering of BixTey nanostructures of above morphologies using six different laser wavelengths. The BixTey nanostructures exhibit the most intense infrared (IR) active A1u mode at 120 cm–1 in the Raman spectra, which disperses with a change in the chemical composition and laser power. In addition, we observe new internal strain-induced peaks in the Raman spectra of BixTey nanostructures. The rich morphologies and compositions present within the nanostructured Bi–Te compounds are expected to result in novel thermoelectric materials.